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This question is about how small the interstellar density is (less than 1 atom per cubic centimeter).

But although the interstellar density is very low, matter tends to extremely aggregate in certain clusters within and through the whole universe (we call them e.g. galaxies, solar systems and planets). Of course this is explained in traditional physics by gravitational attraction of matter on itself.

Are there other current theories - than gravitational attraction of matter - which explain the reason for the extremely clustered accumulation of matter in the universe?

Addendum:

If gravitational attraction of matter was the only reason for the existence of the universe, why isn't the universe just a big clumb of matter since the big-bang (which btw is proven due to the expanding universe)? Doesn't the expanding universe and its deduced big-bang prove that there must be certain invisible processes in the universe which we know nothing about whatsoever? And that these processes tend to organize matter - maybe even create matter in the first place?

Marcus
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Gravity acting on both matter and dark matter is the only candidate in mainstream physics for the force that determines the large scale structure of the universe (although the electromagnetic force may also influence smaller scale structures within individual galaxies).

The early universe was not completely smooth. Primordial fluctuations in density that formed the seeds for the first galaxies have been observed in the cosmic microwave background. The origin of these density fluctuations was quantum fluctuations magnified enormously by the brief period of cosmic inflation very shortly after the Big Bang.

gandalf61
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